1. Field of the Invention
The present invention relates to an ozone gas concentration measurement method, an ozone gas concentration measurement system, and a substrate processing apparatus, and in particular relates to an ozone gas concentration measurement method for use in producing ozone gas from oxygen gas.
2. Description of the Related Art
If a plasma processing, for example, a plasma etching processing is carried out on a wafer as a substrate using plasma produced from a carbon fluorine CF-type process gas, CF-type deposit resulting from the CF-type process gas may become attached to the wafer. The CF-type deposit attached to a surface of the wafer is removed by sputtering using plasma (positive ions), but the CF-type deposit attached to an edge (bevel portion) of the wafer cannot be removed because the bevel portion resists sputtering by plasma.
To cope with this, the CF-type deposit attached to the bevel portion of the wafer is removed using a postprocessing apparatus. Specifically, the postprocessing apparatus heats the bevel portion of the wafer by irradiation with laser light, and supplies ozone gas toward the bevel portion so that the CF-type deposit can be decomposed into CO, CO2, and F2 through a chemical reaction and removed. The degree of the decomposition of the CF-type deposit depends on the concentration of the supplied ozone gas, and hence in the postprocessing apparatus, the concentration of the supplied ozone gas has to be measured and adjusted.
Because ozone gas absorbs ultraviolet rays, there has conventionally been used a method in which a mixed gas containing ozone gas is irradiated with ultraviolet rays using an ultraviolet lamp, and the concentration of ozone gas is calculated and measured based on the degree to which the ultraviolet rays are absorbed (see, for example, Japanese Laid-Open Patent Publication (Kokai) No. 2004-163293).
However, the life expectancy of the ultraviolet lamp is as short as about one year, and moreover, a certain amount of time is required before the ultraviolet lamp is able to irradiate stable ultraviolet rays. Further, if the ultraviolet lamp is continuously used for a long time, the amount of luminescence gradually decreases, and hence the ultraviolet lamp has to be calibrated every one week. Thus, there is the problem that the method of measuring the concentration of the ozone gas using the ultraviolet lamp is inconvenient.